Synchronizing system



' G. GUANELLA SYNCHRONIZING SYSTEM Feb. 18, 1941.

Filed Feb. l0, 1959 5 sheets-sheet i ATTORNEY Feb. 18, 1941. G. GUANELLA2,231,998

SYNCHRONIZING SYSTEM ATTORNEY.

Feb. 18, 1 941. G. GUANELLA SYNCHRONIZING SYSTEM 5 sheet-sheet 5 FiledFeb. lO, 1939 SWEEP OSCILLATOR Fig: 6

1N VENT OR. j usav- (g ua nella M /fek ATTORNEY.

Feb. 18, 1941. G, GUA'NELLA y 2,231,998

sYNcHRoNIzING SYSTEM Filed Feb. 1o, 1959 5 sheets-s116994 j; `.V m-h-"iswEEP 10 l 50 Te oscxLLAToR 1N VENTOR.

ATTORNEY.

` Patented Feb. 18, 1941 PATENT OFFICE SYNCHRONIZING SYSTEM GustavGuanella, Zurich, Switzerland, assignor to Radio Patents Corporation, acorporation of New York Application February 10, 1939, Serial No.255,608 In Switzerland February 17, 1938 10 Claims.

The present invention relates to novel means for and a method ofmaintaining synchronism between transmitting and receiving apparatus intelegraphy. television and the similar transmission systems.

In the transmission of television signals it is customary to apply aspecial control potential to the devices for scanning and reproducing apicture, such potential determining at each instant the position of theimage point within the total image area being transmitted.

Usually there is provided for this purpose an image sweep or deflectingpotential determining the position of each line of the image beingscanned and a line sweep potential to determine the position of eachimage point within the individual scanning lines. These sweep potentialsare produced either by special relaxation oscillators or by convertingor distorting a determined control potential which latter may be derivedby stepping up or down a fundamental frequency.

In order to ensure satisfactory transmission, equality of both frequencyand phase known as locked synchronism between corresponding sweeppotentials at the transmitter and receiver is required. This synchronismis usually obtained by controlling the sweep potential generated at thereceiver by special synchronising impulses received together with theimage signals or alternatively by 3o deriving the sweep potentials atthe transmitting and receiving stations from equal alternating controlpotentials.

The known methods of synchronization have many drawbacks due primarilyamong other reasons to frequent disturbances and impairment of thesynchronism by short momentary interfering impulses especially whenusing relaxation or sawtooth type sweep oscillations. There are otherdimculties in ensuring synchronous operation when employing controlpotentials produced by multiplication from a lower fundamentalfrequency. y

According to the present invention, the difliculties and drawbacksinherent-in the known synchronizing systems are substantially overcomeby the provision of a novel method and system based on the principle ofmutual modulation of a pair of electrical signals one of whichcorresponds to or'is derived from the synchronizing signals while theother corresponds to the deflecting or sweep potential to besynchronized. After suflicient illtering of the modulation product oroutput potential obtained in this manner, there may be derived from thelatter a control potential varying in proportion to small deviationsfrom the syn- (ci. ris-sas) chronism between the transmitting andreceiving devices both as to magnitude and sign. This control potentialis utilized to govern an element determinative of the frequency and/orphase of the deflecting potential produced by the sweep oscil- 5 latorin such a manner as to counteract the initial tendency to deviate fromthe synchronous condition. By suilicient filtering of the controlpotential obtained in this manner the effect of momentary disturbancesliable to impair or interfere with 10 the fidelity of the imagetransmission may be substantially eliminated in practice. As a resultthere is obtained a highly steady and stable synchronizationsubstantially independent of momentary disturbances in the transmissionsuch as 15 occasioned by distorted or mutilated synchronizing impulsesand due to other causes.

The novel method to be described in detail hereafter is suited ingeneral for maintaining synchronism between a pair of sweep potentialgenerators in television apparatus by the aid of synchronizing signalsor impulses transmitted during interrupting pauses between the imagesignals or superimposed upon or otherwise combined with the imagesignals for simultaneous transmission. The inventive method however hasmany other uses such as for maintaining the synchronism between aplurality of scanning arrangements by the aid of a common timing signalor standard controlling frequency. In this manner it is possible tooperate in synchronism several scanning devices which may be arranged atdistant places either simultaneously or in succession. As is understood,'the inventive method is not limited to 35 the use in television butapplies with equal advantage to the transmission of single or stillpictures such as in the case of facsimile transmission or picturetelegraphy.

The invention will become more apparent from the following detaileddescription taken with reference to the accompanying drawings formingpart of this specification and` wherein:

Figures 1 and 2 represent theoretical diagrams and graphs, respectively,explanatory of the basic 45 principle and function of the invention,

Figure 3 is a block diagram illustrating a basic synchronizing system inaccordance with the invention,

Figure 4 is a more detailed diagram showing a 50 modification of asynchronizing system according y to the invention,

Figure 5 is similar to Figure 3 illustrating the employment of amulti-grid electron tube for producing a potential for controlling thesynchronism, 55

Figure 6 shows a further modification embodying a balanced modulator forproducing the control potential, Y

Figure? illustrates a further modication employing an interruptingsystem for generating the taneously synchronizing a plurality of devicesbyv the method and arrangements according to the invention.

Similar reference characters identify similar elements throughout thediierent views of the drawings.

Referring to Figure la, there are shown synchronizing impulses u varyingbetween amplitude levels A0 and A, and having a length T, and spacingintervals To. The impulses u constitute synchronizing signals which maybe transmitted to the receiver during special interrupting pauses of thepicture signals such as at the end oi each line or image and aresegregated at the receiver from the image signals by means of amplitudefilters or in any other suitable manner. In Figure 1b there is shown asaw-tooth type deecting potential v of the type usually employed incathode ray scanners although not limited thereto and varying betweenamplitudes -Bi and -l-Bi. 'Ihe frequency or phase of this potential isto be adjusted in dependence upon an electric controlling potential orcurrent in a manner to maintain absolute or locked synchronism with theimpulses u, Figure 1. There is indicated by the dotted curve m in Figure1b a slight deviation from synchronism, the curve vi lagging the curveou which latter corresponds to the condition of synchronism by a deinitephase difference T between the fundamental frequency components of thecurves.

The generation of a potential for controlling the synchronism is eectedaccording to the invention by mutually inter-modul'ating the deilectingvpotential shown in Figure 1b with the synchronizing or impulsepotential, Figure 1a, and subsequent illtering of the resultant orproduct obtained by such modulation. As a result, there is obtained adirect potential varying in both magnitude and sign in dependence upondeviations from synchronism between the component potentials u and oapplied to the modulating device. By intermodulation of the impulsepotential u v(Figure la) and the saw-tooth potential v` (Figure 1b)there is obtained, when neglecting a constant factor, a product c=u.v asshown in Figure 1c. In case 'of synchronism, the modulation product hasa shape as shown at co resulting from the impulses u and the saw-toothvoltage v0. This product is zero as long as the amplitude A0 of thesynchronizing impulses u is zero; i. e. during the spacing intervalsbetween the impulses. During the impulse periods, however,co eqiialsAnon; that is, the product cu is proportional to v and passes throughzero simultaneously with the latter.

If, now for instance, the saw-tooth voltage, in case of disturbedsynchronism, lags the synchronizing impulses as shown by the dashed linevi in Figure 1b, there is produced bythe intermodulation Aprocessbetween u and v1, a modulation product ci=u.vi. This product is alsozero during'the spacing'intervals between the synchronizing signals.-During thejimpulse periods, however, this modulation product deviatesfrom co due to the fact that v1 assumes higher values than vo. Afteradequate nltering of the modulation products co or ci there are obtainedaverage or direct current components es or er, respectively. Due to thesymmetrical shape of the product potential cu with respect to the zeroline, the component e0 is equal to zero. On the other hand, since theproduct ci is predominantly positive, the mean value er will also bepositive. I1' the saw-tooth voltage v leads the impulses u, the productci will be predominantly negative and accordingly its mean value willalso be negative. Thus, the nltered intermodulation product el variesboth in sign and magnitude proportionately to relative phasedeviationsbetween the saw-tooth voltage and the time spaced synchronizingimpulses.

In accordance with the present invention the controlling magnitude e1 isutilized to control a device adapted to accelerate or decelerate thesawtooth voltage in proportion to and depending on the polarity of thecontrolling magnitude. In this manner an initial phase deviation betweenthe impulse and saw-tooth voltages from a normal phase diierence willeect a change in the sawtooth generator in such a manner as tocounteract the'initial phase deviation; that is, any disturbance of thesynchronism will result in reduction of the disturbance.

y The control oi' the saw-tooth voltage generator by the magnitude e1 iselected by controlling a "frequency or phase determining elementassociated with the generator and adapted to be regulated by the controlcurrent or potential e1 as will be described in further detail withreference to Figures 8 and 9.

An essential feature ot the invention is the fact that the same does notpropose to excite or accelerate a relaxation discharge directly by thesynchronizing impulses, but involves the generation of a separatecontrolling or synchronizing current or potential produced byintermodulation of a pair of potentials having a predetermined relationto the synchronizing impulses and to the saw tooth voltage to bemaintained in locked synchronism. The process of intermodulation of themagnitudes u and v for generating a modulation product c will beexplained further in connection with Figures 5 and 'l of the drawings.

Depending on the particular kind of modulation used there are 'obtainedadditional components in the modulation product ci which however resultsin a mean value or'direct current of constant value so that its effecton the control may be disregarded or eliminated.

The potentials u and o to be modulated may also contain a determinedadditional direct current component in winch case the modulation productwill include only additional alternating potentials and in some cases adirect current component of constant magnitude. The relation ot thefiltered control potential to the deviations from synchronism willremain substantially the same except for a displacement oi' .the zerooperating point.y This will be further understood from the following.

The synchronizing impulses u may be decomposed according to Fourier'stheory into the folaasaees lowing frequency components, assuming thecenter of an impulse as the starting point:

The sweep potential v on the other hand is composed of componentfrequencies as follows:

In the above equations w represents the fundamental frequency of bothsignals, T the ph se displacement of the deflecting potential v relat veto its normal phase position as determined by the synchronizing impulsesu. The positive coefficients an and bn represent the amplitudes of theindividual components whose magnitudes decrease as the order of nincreases.

The direct current component c of the modulation product uv includesonl'y portions derived from components of like frequency of the originalsignals u and v, since as is well understood no direct current componentor beat frequency zero may be generated by modulating currents of unlikefrequency:

Furthermore, the direct current components ao and bo of the originalsignals produce a constant factor an bo of the controlling potential cwhich, if desired, may be eliminatedby suitable compensating means.

For small deviations of synchronism or phase differences T the sign nwTmay be replaced in a known manner by the arc or angle nwT. From this itfollows that the controlling potential c is directly proportional tosmall phase deviations T both as regards its magnitude and sign. 'I'hisrelationship is maintained also in the case that all or some of theamplitudes an and bn of the individual components are modified prior tothe modulation. In case of greater phase deviations, a proportionalrelationship no longer exists since in this case the sign is no longerequal to the corresponding arc or angle.

In the known modulation devices or circuits there are obtainedadditional potentials besides the modulation product uv. Thus, theoutput potential may contain the squares of the input po tentials beingmodulated. 'I'hese potentials u2 and v2 contain direct currentcomponents a02, ai, be2. 1212 which latter, however, are independent ofthe phase deviations T so that their eiect may be eliminated.

Referring to Figure 2a. there is shown the relation between thecontrolling potential e obtained from the signals u and v by mutualmodulation and subsequent filtering in dependence upon relative phasevariations between these potentials. The phase differences are measuredas fractions T/To of an entire period To of the potentials. From thisdiagram it is evident that small deviations from synchronism result inthe production of a large controlling potential due to the great slopeof the curve for small values of T/Tn. However, a suitable controlpotential may also be obtained with larger phase deviations up toT/To=to 1/2. In case of still greater deviations, the phase of thecontrolling potential is reversed, that is the synchronism is controlledwith a phase difference of one or more periods.

In practice it is possible to pass either or both of the potentials tobe modulated through nonlinear or distorting circuits or devices priorto their application to the modulating device or circuit. -'I'bus forinstance the signal according to Figure 1b may be converted by means ofan amplitude limiting device into a signal according to Figure ld fromwhich there is also obtained by modulation with the signal according toFigure la and subsequent filtering a controlling potential varying indirect proportion to small phase dierences both as to its magnitude andsign as shown by the graph according to Figure 2b. The modulation of thepotentials may be effected by applying them to a device or circuit whosetransmission factor or electrical conductivity may be controlled inlinear dependence upon a further potential such as is the case in theknown amplitude modulation devices or circuits. However, it is alsopossible for the purpose of this invention to employ a modulating systemproducing a more or less distorted output potential. Thus, asatisfactory controlling potential may be obtained by the use ofcircuits including elements having non-linear impedance characteristicsor whose transmission. factor or conductivity varies in non-lineardependence upon an impressed controlling potential.

According to a further embodiment, the sum and difference of the twopotentials u and v may be formed in a push-pull or balanced modulatingcircuit by means of rectiers of the square law or any other typewhereupon by sunicient filtering of the differential of the rectifiedpotentials a satisfactory direct current component for controlling thesynchronism may be obtained. Furthermore, the controlling potential maybe produced by an inertialess switching device or circuit interruptingor reversing the signal o in the rhythm of the synchronizing impulses u.Such an inertialess switch may have the form of a chopping circuitcomposed of rectiiiers whose conductivity is controlled in accordancewith the impulses u.

The potentials to be modulated may also be modified prior to themodulation in such a manner that individual components thereof are phaserotated by a predetermined angle. In this manner potentials may beformed which are specifically suited for the particular type ofmodulation being used. In many cases potentials having -phase rotatedcomponents may be directly dethe impulse signal u is rotated in phase byan amount pn and that the nth component of the sweep potential v isphase rotated by an angle qn. The potentials obtained after such phaserotation may be represented by the following expressions:

n i -b sin(3w(tT)-q)(5) from which the direct current component of themodulation product is obtained as follows:

=b b' T +1.22b2'2T 2 2 c ao 0+ ),al l smug iag sfnSm/lL-liqsllll) (p6;This component is characteristic of the phase deviations T/To if it canbe replaced by the expression (3) that is if the difference between thephase displacements qn-pn disappears for all frequency components or ifthis difference for all the components is divisible by 360. In all thesecases the phase difference between components of like frequency of thetwo potentials remains unchanged relative to the phase differencebetween components of like frequency of the synchronizing impulsesresulting in a controlling potential c as represented by the expression(3i eventually with changed amplitudes an, bn.

'I'he expression (6) will also remain characteristic of the phasedeviations if the differences between the phase displacements qxl-pn areanA uneven multiple of 180. This corresponds to a. reversal of thepolarity of all components of c excepting the constant factor as bo.After considering this phase reversal there is obtained a controllingpotential varying `in direct propor. tion to small phase deviations bothas to its magnitude and sign. As is understood it is immaterial whetherthe above phase displacement by 180 or a multiple thereof is due to arotation of the components of the synchronizing impulses or of the sweeppotential and whether the components of like frequency of bothpotentials are rotated by amounts equal to zero or 180. The

latter case prevails for instance if all the components are shifted by90. Such a phase rotation may be effected by using phase shifting net-`works' as shown at 20 and 23 in Figure 4 to be described hereafter.Moreover, a change of the amplitudes of the individual components maytake place simultaneously with their phase rotation.

According to a further feature of the invention it is possible toutilize the fundamental components of the signals to be modulated bysuitable filtering or elimination of higher harmonics thereof. Thus, themodulating circuit may be controlled by a sinusoidal potential derivedfrom the sweep potential o by sumcient filtering, or alternatively asinusoidal potential from which the sweep potential is produced by'distortion in a known manner may be applied to the modulating device orcircuit.

Several practical embodiments of modulating arrangements suited for thepurpose of the invention are illustrated in Figures 3 to 9 of thedrawings.

Referring to Figure 3, there is shown in block diagram form a basicsynchronizing arrangement constructed in accordance with the invention.There is indicated by I a sweep potential generator which may be arelaxation oscillator of known type or any other suitable arrangementfor generating a saw-tooth shaped deflecting potential v of the type asshown in Figure 1b. This defiecting potential is applied through linesII upon a scanning device or image reproducer to be connected toterminals I2. The same potential is applied through lines I3 to themodulation device or circuit I4 which in addition is controlled by afurther input potential corresponding to the synchronizing signals uaccording to Figure la and applied to terminals I5. The potentialobtained by mutual modulation of these two potentials is filtered by asuitable arrangement embodied in I4 whereupon the filtered potential edeprived of all higher harmonics is impressed upon the sweep oscillatorI0 through lines or circuit I6. The sweep oscillator is affected by thiscontrol potential in such a manner as to vary the frequency of the sweepvoltage v impressed upon the output -I2 4in dependence upon variationsof the controlling potential e in such a manner as to maintainsynchronism between the potentials v' and u in the manner described andunderstood from the foregoing. If at a definite instant the sweeppotential v leads the synchronizing impulses u a controlling potentialis produced by the modulation of the two potentials in 14 acting toinfluence the sweep oscillator in a manner to retard v and to restorethe synchronism. In an analogous manner a control takes place Iin thereverse sense if the sweep potential v lags the synchronizing potentialu.

The sweep oscillator I0 in Figure 3 may also be of the type functioningby converting an alternating potential w of standard frequency appliedthereto through terminals Il into the desired sawtooth potential v. Inthe latter case, the frequency of v is determined by the frequency of w.the ratio between them being a whole number if frequency transformationis employed. Thus, the potential w may be a low frequency potential sentto the image transmitter and receiver through special lines such as thealternating potential derived from a standard power or lighting system.In the latter case, the frequencies of the synchronizing impulses u andof the deflecting signals 'o are alike, but a considerable phasedifference may exist therebetween d e to unequal phase rotation causedby the lighting circuits. These deviations or phase differences may beeliminated by utilizing a system according to the invention whereby thephase of the potential received from a power line and converted in I0 iscontrolled by the potential e in a manner to reduce or eliminate thephase shift effected by the line. Experiments have shown that smallphase shifts of the potential w result in comparatively large phaserotations of the output potential v of higher frequency. For this reasonit is advisable to pass the input potential w prior to its stepping upto a higher frequency through a circuit whose phase characteristic isvaried by the controlling potential e.

The time constant of the filtering devices embodied in I4 should beadapted as far as possible to the frequency or phase variations to beexpected in practice. If the relative frequency variations between u andv are of a slow character, a large time constant should be employed. Inthis manner the frequency or phase of v is prevented from being subjectto rapid variations by momentary disturbances or mutilationsy of thesynchronizing signals. On the other hand, in case of a less stablefrequency of the sweep or synchronizing potentials considerabledeviations from synchronism may occur by excessive ltering of thecontrolling potential which may be reduced or eliminated by use of adecreased time constant.

Referring to Figure 4 there is shown an embodiment for modulating twopotentials which have been changed previously by means of nonlinear orphase shifting elements. The impulse generator I8 may be a relaxationoscillator producing an impulse potential v' of the type shown in Figurela. From this impulse potential there is derived a saw-tooth shapedeecting potential o, Figure 1b, by the aid of a phase shifting or delaynetwork 20 comprising a large resistance 2| and large capacity 22 inseries and connected across the output of the generator I8. The capacity22 is charged through the resistance 2| whereby there is obtained at theterminals I9 of the former a saw-tooth potential of the type shown inFigure lb. The synchronizing impulses u are impressed across terminals Iupon a further phase shifting or delay network 23 comprising alarge'inductance 24 in series with a small ohmic resistance 25, wherebythe potential at the latter will assume a saw-tooth shape of the typeshown in Figure lb.

In an arrangement of the type described in the preceding paragraph, thecontrolling potential e may be obtained by modulating the synchronizingpotential u with the deflecting potential v in the manner describedhereinabove. Alternatively, the control potential may be derived bymodulation of the -two potentials u' and v, due to the fact that therespective components of these potentials comply with the aboverequirement as regards their phase and since one of these potentials hasthe form of impulses according to Figure 1a and the other is ofsaw-tooth shape according to Figure 1b.

Moreover, the saw-tooth potential u' may be modified by an amplitudelimiting circuit 26 restricting its amplitudes by shunting through apair of rectiflers 21 and 28 in series with counter biasing batteries 29and 30, respectively. In this oase, there are applied to the modulatingdevice I4 potentials u" and v of the type shown in Figures la and 1d,respectively, resulting in the generation of a controlling potential evarying in dependence upon deviations from the synchronism in the mannershown in Figure 2b.

In Figures 5, 6 and 7 there are shown by Way of example variousmodulating arrangements suited for the purpose of the invention.According to Figure 5 the potentials u and v are applied to separategrids 34 and 35, respectively, of a multi-grid electron tube 36, thegrids being preferably separated by a positively biased screen, wherebyin a known manner aproduct output potential may be derived from theresistance 31 connected in the plate output circuit. This outputpotential in the example shown is impressed upon a smoothing illternetwork comprising a series resistance 39 and a parallel capacity 38 toobtain potential e for controlling the synchronism of the sweeposcillator I0 in a manner described hereinbefore.

According to the embodiment shown in Figure 6 modulation of thepotentials u and v is eifected by separate rectification of the sum anddifference thereof and utilization of the differential of the rectifiedpotentials. There is provided for this purpose a balanced modulatorcomprising in the example shown an induction coil 42, the oppositehalves of which form a Wheatstone bridge circuit together with a pair ofrectifiers 44 and 45 each of the latter being provided with a seriescondenser 46 and 41, respectively. The dei'lecting potential 2v of twicethe amplitude is impressed upon terminals a, b of the inductance 42while the synchronizing potential u is applied to the center e of theinductance 42 on the one hand and to the junction point f of therectifiers 44 and 45. The remaining terminals of the rectiers c, d areconnected to the sweep oscillator I6 through a lter network comprisingseries resistances 48 and 49 and a shunt capacity 50. In an arrangementof this type there is produced between the terminals a and f the sumpotential u-l-v and between terminals b and ,f the difference potentialu-v. These sum and difference potentials are rectified by the rectiflers44 and 45, respectively, thereby charging the condensers 46 and 41. Thedifferential between the rectied potentials appearing between c and d isimpressed upon the filter 48, 49, 50, obtaining in this manner a directoutput potential e varying both as to sign and magnitude in dependenceupon deviations from synchronism between the potentials u and vin themanner understood from the above.

In a circuit of the foregoing type the position of the rectiflers 44, 45and the condensers 46, 41 may be exchanged without affecting thefunction and operation.

Referring to Figure 7 there is shown a modulating system of theinterrupting type comprising inductance 42 similar to Figure 6 forming abridge circuit together with a pair of resistances 54 and 55, the latterhaving in series therewith rectifiers 56 and 51, respectively. Thedeflecting potential v is again applied to the terminals a, b of the in-5 ductance 42 while the synchronizing signals are impressed upon thecenter point e of the inductance 42 on the one hand and upon thejunction f between the resistances 54 and 55. The rest of the circuit issubstantially similar to the circuit according to Figure 6. During theinterval between the impulses u, a negative impulse potential isimpressed through impedances 54, 55 4in the blocking direction of therectiilers 56, 51, whereby the latter prevent passage of the sweep orsaw- 15 tooth potential v. During the impulse periods on the other hand,a corresponding impulse current will ow through4 the rectiiiers, wherebythe potential vis passed to terminals c, d. The function of the rectiersis therefore to periodically interrupt the saw-tooth signal v in therhythm of the synchronizing impulses u.. After adequate filtering in 48,49, 50 of the interrupted output there is obtained a control potential eadapted to maintain the synchronism of the oscillator I0 insubstantially the same manner as described hereinbefore.

The control of the sweep or deecting potential oscillator by thesynchronizing potential may be eected in various manners. When using arelaxation oscillator the frequency of the relaxation oscillations isdependent upon the values of the various impedances and operatingvoltages as is well known. It is possible therefore to control thefrequency of such an oscillator by varying a suitable impedance oroperating voltage in dependence upon the synchronizing potential in sucha manner as to restore synchronous frequency or phase conditions. Thus,for instance a nonlinear impedance may be provided in the oscillatorcircuit capable of being controlled by a biasing potential or currentsuch as a vacuum tube impedance or the like. Practical embodiments ofsuch arrangements are shown by way of example in Figures 8 and 9.

lReferring to Figure 8, there is shown a relaxation oscillator of knowntype comprising a gaseous triode shunted by a condenser 62 and connectedin series with a source of potential 64, an impedance such as aresistance 63 and the anodecathode path of further triode 60 which maybe of the high vacuum type. Disregarding the triode 60 for the moment,this arrangement constitutes a known relaxation oscillator `in that thecondenser 62 is charged through impedance 63 gradually until the gasdischarge through tube 6I is initiated, whereby the potential at thecondenser is suddenly decreased to a value corresponding to theextinguishing potential of the tube. This phenomenon is repeatedperiodically whereby there is obtained at the output terminal 66 asaw-tooth shaped relaxation potential, the Dl C. component of which maybe adjusted by means of a potentiometer 61 in shunt to the source 64.'I'he initiation of the discharge may be controlled within substantiallimits by varying the grid potential of the tube 6I applied throughinput terminals 68. It is furthermore possible to vary the chargingperiod by an adjustment of the charging resistance such as the impedanceof the triode 60 in the example illustrated. The triode 60 constitutes avariable impedance which may be controlled by varying its grid potentialapplied through input terminals 69. It is thus possibleV to control thefrequency of the relaxation oscilla- 76 tions by the synchronizingpotential e by impressing the latter upon the grid of either the tube 80or 8|. f

If the sweep potential is generated by converting a local sinusoidalpotential the former may be regulated by controlling the frequency ofthis local potential. 'I'his may be effected by varying the tuning of analternating current generator such as by varying an adjustable reactiveimped- 10 ance associated with a tuning element. Such a reactiveimpedance may have the form of an electron tube constituting anadjustable inductive and capacitative reactance in a suitable circuit ofwell known design such as commonly used in automatic frequency ortuning, control systems (AFC).

According to a further embodiment, the phase position of an alternatingpotential controlling a sweep oscillator fromy the outside may becontrolled in dependence upon the synchronizing potential e by suitablephase shifting networks or devices. A suitable arrangement of this typeis shown in Figure 9. In the latter the alternating potential w whosephase is to be controlled is impressed through terminals 13 upon a pairof phase rotating networks the first of which comprises a condenser 14-in series with a resistance 15, while the second network comprises aninductance 16 in series with a resistance 11. v The junction 3 pointsbetween the inductive and reactive impedances of these networks areconnected to the outer grids of a pair of electron tubes 18 and 19,respectively, whereby the alternating potentials impressed upon thesegrids are either lagging or heading relative to the input potential w.The

amplication of the tubes 18 and 19 is furthermore controlled by thepotential e impressed upon a pair of further grids of the tubes in phaseopposition through input terminals 80 in such a manner that an increaseof the amplification of one tube corresponds to a decrease of theamplifi- -cation of the other tube. As aresult, the output orplatef'potentials derived at terminals 84 through coupling condensers 82and 83 is composed of adjustable components of the leading or lagginginput potentials, whereby the phase of the resultant output potential at84 relative to the input potential applied at 13 is proportional to thesynchronizing potential e impressed upon terminals 80. 'Ihe phaseadjusted output potential may.

` 00 according to Figure 9 the frequency of the control potential maynot be varied if the phase rotation'is effective within narrow limitsonly. For this reason, arrangements of this type may be used only ifequal control frequencies are employed for generating the sweeppotentials at the transmitter and at the receiver, whereby thesynchronizing system merely serves to correct phase deviations betweenthe controlling frequencies such as due to unequal impedancecharacteristics' 0 of the lines or networks transmitting the controllingfrequency to the transmitter and receiver, respectively.

In Figure 10 there is shown in block diagram form a complete televisionreceiving system embodying the improvement according to the invention.Item represents the amplifier having input terminals 88 to which arei'ed the received image signals in the form oi' a modulated carrier wavetransmitted through a line or through space after previous amplificationat RF and 1F fre- 5 quency. From the power or output stage 81 of theamplifier 85 the modulated intermediate frequency signals are fed to arectifier 88 serving to segregate the image 'signals which latter areapplied to an intensity controlling element of a 10 scanning device suchas a cathode ray tube 90 in the example shown. A portion of the outputenergy is further fed from the power stage 81 to an amplitude filter 9|serving to segregate the synchronizing impulses u (line and image sweep15 impulses) in a manner well known. 'I'hese impulses are applied to apair of modulators 93 and 94 serving to produce controlling potentials efor maintaining the synchronism of the sweep oscillator 95 and 96,',respectively, as described by the 20 present invention. Oscillator 95may serve to produce the image sweep potential and oscillator 96 mayserve for producing the line sweep potential applied to two pairs ofdefiecting plates |00 and |0|, respectively, of the cathode ray tube 9025 in a manner well understood. Thus, modulator 93 serves for modulatingthe image sweep potential with the image sweep impulses resulting in acontrolling potential at the output 91 applied to the image sweeposcillator 95 to control the syn- 30 chronism thereof. The line sweepimpulses simultaneously applied to the modulator 93 will have no effectupon the synchronism due to the fact that the controlling outputpotential is sui'llclently filtered thereby preventing momentarydisturb- 35 ances from affecting the sweep oscillator 95. In

a similar manner the modulator 94 serves to produce a controllingpotential for maintaining the synchronism of the line sweep oscillator96. This controlling potential is unaffected by the image 40 sweepimpulses simultaneously applied to the modulator 94 due to the fact thatthe resulting disturbing potentials caused by these impulses whosedirect current component taken over a long time and period is equal tozero may be sub- 45 stantially suppressed by suilicient filtering of thecontrolling potential.

Referring to Figure 11, therel is shown an embodiment for simultaneouslycontrolling the synchronism of several scanning devices by the aid 50 ofa controlling or timing frequency. There is provided for this purpose animpulse generator |03 the output of which is applied to a pair ofmodulators |06 and |01 each of which serves to control the/synchronismof an associated scanning 55 device |08 and |09 by influencing therespective sweep oscillators |04 and |05 in a manner readily understoodfrom the foregoing.

It will be evident from the above that the invention is not limited tothe specic arrangements 60 and steps described herein for illustration,but that the underlying thought and inventive principle are susceptibleof numerous embodiments and modifications coming within the broad scopeof the invention as defined in the appended claims. 55 The specificationand drawings are to be regarded, therefore, inan illustrative ratherthan a limiting sense.

I claim:

1. In television, the method of synchronizing a 70 saw-tooth scanningpotential by means of periodic synchronizing impulses, comprising thesteps of intermodulating said saw-tooth potential' with said impulses toproduce a product function resultant potential, deriving from saidproduct po- 75 function potential, deriving from said product po-`tential a direct component varying in sign and magnitude in proportionto deviations of said sawtooth potential from synchronism with saidimpulses, and utilizing said direct component to control said saw-tooihpotential to maintain the same in locked synchronism with said impulses.

3. In a television system, a saw-tooth scanning' oscillator, a source ofsynchronizing impulses, means for maintaining locked synchronism betweensaid oscillator and said impulses comprising a modulating device adaptedto produce 'a product function potential from potentials derived fromsaid oscillator and said synchronizing impulses, filter means forderiving a direct component from said product potential varying in signand magnitude in dependence upon deviations of the oscillator frequencyfrom synchronism with said impulses, and means for impressing saiddirect component upon a frequency determining element of said oscillatorto compensate for deviations from synchronism with said impulses.

4. In a system as claimed in claim 3 including means to limit theamplitude of said derived potential to a predetermined value.

5. In a system as claimed in claim 3 wherein said modulating means iscomprised of a multigrid electronic device, said derived potential and40 said synchronizing impulses being impressed upon diierent grids ofsaid tube.

6. Ina television system, a saw-tooth scanning oscillator comprising acharging impedance in series with a condenser shunted by a gaseous dis-45 charge device, a grid for said device, a source oi' synchronizingimpulses, means for maintaining locked synchronism between saidoscillator and said impulses, said means comprising a modulating devicefor producing a product function poten- 50 tial from potentials derivedfrom said oscillator and said synchronizing impulses, further meansincluding filter means for deriving a direct potential from said productpotential varying in magnitude and sign in dependence upon deviations of55 the oscillator frequency from synchronism with said impulses, andmeans for impressing said direct potential upon said grid electrode tocontrol the frequency of said oscillator to compensate for deviationsfrom synchronism with said impulses.

'7. In an electrical system, a Isaw-tooth signal generator, a source oftime spaced periodic impulse signals, means for maintaining saidgenerator in locked synchronism with said impulse signals, said meanscomprising a. modulating de- 65 vice, means for applying to saidmodulating device a pair of potentials derived from said saw-tooth andimpulse signals, respectively, means including filter means for derivingfrom the intermodulation product of said device control energy varyingin sense and magnitude proportionately to deviations of the saw-toothsignals from synchronism with said impulse signals, and means forcontrolling said saw-tooth generator by said control energy to restorethe synchronism thereof with said impulse signals.

8. In an electrical system, a saw-tooth signal generator comprising aresistance, a condenser in series with said resistance and a gaseousdischarge device shunting said condenser, a control grid for saiddischarge device, a source of. time spaced periodic impulse signals,means for maintaining said saw-tooth generator in locked synchronismwith said impulse signals, said means comprising a modulating device,means for applying to said modulating device a pair of potentialsderived from said saw-tooth signals and said impulse signals,respectively, means including lter means for deriving from theintermodulation product produced by said device control potentialvarying in sense and magnitude proportionately to deviations of thesaw-tooth signals from synchronism with said impulse signals, and meansfor applying said control potential to said grid to control saidgenerator to restore the synchronism of the sawtooth signals with saidimpulse signals.

9. In an electrical system, a saw-tooth signal generator comprising animpedance, a condenser in series with said impedance and a gaseousdischarge device shunting said condenser, at least part of saidimpedance being constituted by an electron discharge tube having acontrol electrode, a source of time spaced periodic impulse signals,means for maintaining said saw-tooth generator in locked synchronismwith said impulse signals, said means comprising a modulating device,means for applying to said modulating device a pair of potentialsderived from the saw-tooth signals and said impulse signals,respectively, means including filter means for deriving from theintermodulation product produced by said device a control potentialvarying in sense and magnitude proportionately to deviations of thesaw-tooth signals from synchronism with said impulse signals, and meansfor impressing said control potential upon said control electrode tocontrol said saw-tooth generator to restore the synchronism of thesawtooth signals produced with said signal impulse signals.

10. In an electrical system, a generator for signal waves constitutedsubstantially by a sine term Fourier series, a source of periodicsignals constituted substantially by a cosine term Fourier series, meansfor maintaining said waves in locked synchronism with said signals, saidmeans comprising a, modulating device, means for applying` to saidmodulating device a pair of potentials derived from said waves and saidsignals, respectively, means including lter means for deriving from theintermodulating product produced by said device control energy varyingin sense and magnitude proportionately to deviations of said waves fromsynchronism with said signals, and means for controlling said generatorby said control energy to restore the synchronism with said periodicsignals.

` GUSTAV GUANELLA.

